The invention pertains to a device for blow-molding containers, which comprises at least one blow-molding station with a blow mold, where the blow mold is held by a carrier of the blow-molding station, and where a pressure zone is sealed off from the environment by a seal.
In container molding by the action of a blowing pressure, parisons of thermoplastic material such a parisons of PET (polyethylene terephthalate) are sent through various processing stations within the blow-molding machine. A blow-molding machine of this type typically comprises a heating device and a blowing device, in the area of which the previously tempered parison is expanded by biaxial orientation to form a container. The expansion takes place with the help of compressed air, which is introduced into the parison to be expanded. The sequence of processing steps carried out during this expansion of the parison is explained in DE-OS 43 40 291. The previously mentioned introduction of the pressurized gas also comprises the introduction of compressed gas into the developing container bubble and the introduction of compressed gas into the parison at the beginning of the blowing step.
The basic design of a blow-molding station for molding containers is described in DE-OS 42 12 583. Possible ways of tempering the parisons are explained in DE-OS 23 52 926.
Inside the blow-molding device, the parisons and the blown containers can be transported by various handling devices. The use of transport mandrels, onto which the parisons are set, has proven to be especially effective. The parisons can also be handled by other types of support devices, however. The use of grippers to handle parisons and the use of spreading mandrels, which can be introduced into the mouth area of the parison to hold it, also number among the available alternatives.
The handling of containers with the use of transfer wheels is described in, for example, DE-OS 199 06 438; here the transfer wheel is arranged between a blowing wheel and a delivery section.
The parisons are handled as previously explained according to one of two different methods. In the case of the so-called two-stage method, the parisons are first produced by injection-molding and then stored temporarily. At a later time, they are thermally conditioned and blown into containers. The second possibility is the so-called one-stage method, in which the parisons are first produced by injection-molding and allowed to harden sufficiently and then immediately blown into containers.
Blowing stations of various designs are known. In the case of blowing stations mounted on rotating transport wheels, mold carriers which can open up like a book are frequently encountered. It is also possible, however, to use mold carriers which can be moved relative to each other or guided in some other way. In the case of stationary blowing stations, which are especially suitable for accepting multiple cavities for container molding, plates arranged parallel to each other are typically used as mold carriers.
According to the prior art, it is known that the connecting elements can be positioned either pneumatically or mechanically by the use of cam controllers. Cam controllers have been proven effective especially in the case of blow-molding machines with rotating blowing wheels, because here, as a function of rotation of the blowing wheel, the individual positions in question can be predefined by the cam controller. The use of these types of cam controllers avoids the additional consumption of compressed air.
In the area of the blowing stations, the blow molds being used are typically supported by mold carriers. The blow molds are usually divided into two side-by-side halves and a bottom mold piece. The mold carriers are typically locked together mechanically or clamped mechanically together. When the parisons are molded into containers by the action of the blowing pressure, care must taken to prevent gaps in the mold, because these could leave an impression on the container.
It is therefore known that at least one of the two halves of the blow mold can be clamped pneumatically against its assigned mold carrier in such a way that the formation of gaps in the mold can be prevented. This can be done, for example, by supplying the blowing pressure simultaneously both to the blowing station and to a pneumatic clamping device, so that, as the internal pressure in the container to be blown increases, the force holding the mold together also increases in the blow mold.
The pneumatic clamping devices which are arranged in the area of the blowing station are typically connected to their assigned control valves by connecting hoses. After a container has been produced but before the blow mold is opened, the internal pressure is released from both the blown container and the pneumatic clamping device. This is typically done with the concomitant use of sound dampers to damp the noise created by the escaping gas.
In the area of the pneumatic clamping devices, at least one cavity is provided, which must be sealed off against the environment. A sealing effect of this type is typically achieved by the use of an elastomeric material, which is realized as a profiled section extending all the way around. An example of a seal of this type is described in, for example, DE 199 29 033.4. Modern blow-molding machines are operated at high outputs per unit time. Production rates of about 2,000 bottles per hour and blow-molding station are normal. There is, however, the desire to increase these production rates even more. For the production of each container, the blow mold is first clamped shut pneumatically, and a corresponding load reversal occurs in the area of the all-around seal. The large number of load reversals leads over time to damage to the sealing material; cracks in the area of the profiled surface are especially common. These surface profilings are desirable, however, because they improve the sealing effect.